Method for acid treating solid supports

ABSTRACT

Process for preparing shaped base materials for use in solid catalysts for commercial processes. The solid contact material is prepared by pre-soaking a porous solid particulate carrier material in an organic liquid, immersing the carrier without drying in a dilute acid solution for a given time interval, washing, drying and calcining the impregnated carrier. After calcination, the carrier is impregnated with an active material.

BACKGROUND OF THE INVENTION

This invention relates to: a process for preparing improved catalyst andsorbent supports; the supports prepared thereby; catalysts and sorbentscomprising these supports; and to processes wherein such catalysts andsorbents are used.

Processes wherein solid contact materials, such as supported catalystsand/or supported sorbents are used, are, of course, well known in theprior art. These include petroleum processes such as catalytic crackingand hydrocracking, reforming and the like and various gas purificationprocesses such as those involving the catalytic conversion of nitrogenoxides in the presence of ammonia or other reducing agent and thoseinvolving the adsorption of sulfur oxides.

As is also well known in the prior art, the activity of many, if notall, of these prior art catalysts and sorbents can be altered, and oftenimproved, by an acid treatment of the carrier or support material eitherbefore or after the same has been shaped. Generally, however, such acidtreatment has adversely affected the strength characteristics of theresulting catalyst or sorbent. This is particularly true with theso-called amorphous carriers such as alumina, silica, titania, zirconia,alumina-silica, silica-alumina and the like. As a result, acid treatmenthas not heretofore, been generally used in the preparation of catalystsand sorbents. It is, therefore, an object of the present invention toprovide a process in which acid treatment could be used to increase theactivity of catalysts and sorbents without adversely affecting theirstrength characteristics.

SUMMARY OF THE INVENTION

In accordance with the present invention, sorbents and catalysts ofimproved activity are prepared. By the present method, the carriermaterial is immersed in a presoak liquid and then in an acid solutionwhich is substantially immiscible with the presoak liquid. Immersion inthe acid solution is controlled so that the carrier material is etchedas desired. Next, the carrier material is removed from the acidsolution, washed to remove the acid, dried and calcined. The calcined,etched carrier material is then impregnated by immersion in animpregnating solution containing a dissolved compound which isdecomposable into a desired active material, dried and the decomposablecompound converted into the desired active material by calcination.

DETAILED DESCRIPTION OF THE INVENTION

The sorbent preparation techniques to be described herein are applicablegenerally to the preparation of porous granular solid contact materials,particularly shaped or extruded materials, comprising a porous carriermaterial and an active material which is deposited on the carrier.

The carrier material which can be used in the preparation of catalystsand sorbents according to this invention are porous materials ingranular or particulate form. The materials are inorganic refractorysubstances, which are preferably hydrophilic so that they can be wettedby polar organic liquids and by aqueous impregnating solutions. Typicalcarrier materials include alumina, silica, silica-alumina, titania,titania-alumina, alumina-zirconia, alumina-thoria, bauxite, magnesia,and the like. Alumina is a preferred carrier material for thepreparation of flue gas desulfurization sorbents, and for othercatalysts and sorbents as well.

The carrier according to the present invention is in the form ofparticles or grains in any desired shape. Conventional shapes such asspheres and cylindrical extrudants can be used. However, best resultsare obtainable when the carrier particle is a more irregular shape, suchas Raschig rings or Intalox saddles, the latter being shown anddescribed in U.S. Pat. Nos. 2,639,909 and 3,060,503. These irregularshapes are preferred because packed beds of these shapes have a highervoid volume with resultant lower pressure drop than packed beds of moreconventional shapes such as spheres and cylinders. The carrier materialscan be formed into particles of desired shape by known techniques suchas extrusion. It is believed, however, that such shaping techniquescause the formation of a low porosity outer layer on the base material.This less porous covering can significantly interfere with the ingressand egress of fluid reactants and products, thus materially reducing theeffectiveness of the catalytic materials. In accordance with the theory,acid treatment techniques are thought to be effective in that theyremove this layer.

The shaped carrier particles which are used in the present invention arecharacterized by a high surface area, generally over 100 square metersper gram, which is due to an internal pore structure. This internal porestructure is well known in the art.

According to the present invention, the carrier particles prior toimpregnation are immersed in a polar organic presoak liquid for a timesufficient to fill substantially completely the pores of the carrier.The quantity of presoak liquid is, of course, greater than the totalpore volume of the carrier being immersed. The total pore volume of thecarrier particles being immersed is computed by multiplying the unitpore volume (i.e. cc/gram) by the quantity (in grams) of carriermaterial. Immersion times of about 10 minutes are sufficient in mostcases to permit the presoak liquid to displace the air in the carrierpores and to fill the pores completely; much shorter times frequentlyare sufficient. Preferred presoak times are in the range of about 10minutes to about 2 hours; longer times are permissible. Immersiontemperatures ordinarily can range from the freezing point to the boilingpoint of the presoak liquid. Room temperature (about 25° C. or 77° F.)is quite desirable in most cases. Lower temperatures increase theviscosity of the presoak liquid and thereby reduce the rate ofdisplacement of the presoak liquid by the acid etching solution.

The presoak liquid must be capable of wetting the carrier material.Carrier materials, such as sponge metals, which are not easily wet, andnonwetting liquids such as mercury, are usually avoided. The presoakliquid must also be capable of displacement by the acid etching solutionat a rate slow enough to permit control of the extent of acid attack.Other criteria which are desirable in a presoak liquid are: (a) chemicalstability; (b) immiscibility or only slight miscibility with the acidsolution (to facilitate removal of the acid solution without significantremoval of the presoak liquid); and (c) a volatility lower than that ofwater but not so low as to hamper its removal during the drying andcalcination steps.

Aliphatic alcohols containing from 4 to 12 carbon atoms and particularlyprimary aliphatic C₅ -C₁₀ monohydric alcohols, are preferred presoakliquids. Normal decyl alcohol is a preferred presoak liquid. Because ofits greater viscosity it is more slowly displaced than the loweralcohols. The etching process is thus better controlled. 1-pentanol is agood presoak liquid. An isomeric mixture composed predominantly ofprimary aliphatic monohydric C₆ alcohols, commonly known as "oxoalcohol," is another good presoak liquid. An isomeric mixture composedpredominantly of primary aliphatic monohydric C₈ alcohols, which is alsocommonly called "oxo alcohol," is also a good presoak liquid. Ingeneral, the C₄ -C₁₂, and especially the C₅ -C₁₀, alcohols are goodorganic presoak liquids. Other classes of organic compounds can also beused as presoak liquids.

The above-named presoak liquids have been found particularly desirablewhen alumina is the carrier material. There is some variability in thechoice of presoak liquids depending on the choice of carrier material,since the readiness with which a presoak liquid is displaced by the acidetching solution is governed in large measure by the degree ofinteraction between the presoak liquid and the carrier material, whichin turn is influenced by the chemical and physical properties of bothpresoak liquid and carrier.

The preshaped carrier particles can be separated from excess presoakliquid by any suitable method, e.g. removal of the carrier particlesfrom the body of liquid, or draining of the presoak liquid from itscontainer. At this point the pores of the carrier are completely filledwith presoak liquid, and some excess liquid may be dragged out of thecontainer of presoak liquid by the carrier. The excess liquid may bedrained or blotted from the carrier if desired, although this is notnecessary. However, it is essential that the carrier not be dried atthis stage. The carrier, without drying is immersed in the acidsolution.

The preferred acids must be capable of wetting and interacting with thecarrier material but being readily separated from the presoak liquid.Strong acids are preferred since they can achieve the desired etching ofthe carrier material. In general, the common inorganic acids aredesirable. These include hydrochloric acid, sulfuric acid, nitric acidand phosphoric acid. Concentrations of about 10% or less are especiallypreferred. Organic acids may also be used if desired. The organic acidused should have a relatively high ionization constant in order toinsure sufficient etching strength. Values for the ionization constant,Ka, of about 1 × 10⁻³ and higher are desirable. Suitable organic acidsinclude chloroacetic acid, trichloroacetic acid, maleic acid, malonicacid and oxalic acid.

While the inventors do not wish to be bound by any particular theory, itis believed that the improvement in activity for the finishedbase-active component combination is due, at least in part, to thecontrolled opening of surface-to-interior pores which had been closedduring the shaping process. This mechanism, of course, should not beconstrued as defining the scope or limitations of the invention, butrather, should be understood as one possible explanation, recognizingthat other mechanisms may well play a major part in the effectiveness ofthis newly discovered procedure.

Once the carrier material has been sufficiently etched, the acid iswashed away without substantially removing the presoak liquid. Thechoice of wash liquid is dependent upon the selection of acid andpresoak liquid. Preferably, water is employed as a washing solution, butacetone and lower molecular weight alcohols such as methanol orisopropanol may also be used.

The impregnating solution contains, at its solute, a compound which isdecomposable into the desired active material. Thus, for example, in thecase of flue gas desulfurization sorbents where the desired activematerial is copper oxide, a copper salt such as copper nitrate may beused as the solute. Where the desired active material is another activematerial, e.g., iron, cobalt, nickel, vanadium, chromium, zinc, cadmium,platinum or palladium, or a compound (usually an oxide) thereof, adecomposable salt of the desired metal is chosen as the solute of theimpregnating solution. Ferric nitrate, cobalt nitrate, nickel nitrate,platinum chloride, and palladium chloride are examples of suitabledecomposable salts. In general, the desired active material is a metal,a metal oxide, or a mixture of metals or metal oxides, and the solute ordecomposable compound is correspondingly a metal salt or a mixture ofmetal salts. Suitable decomposable metal salts yielding virtually anydesired metal oxide are known in the art. The solvent of theimpregnating solution is usually water, which has the advantage of lowcost and high affinity for the usual carrier materials. Thus, thepreferred impregnating solutions are aqueous solutions. However,solvents other than water may be used where desired, provided thedesired decomposable compound is soluble therein. Suitable nonaqueoussolvents include methanol, ethanol, isopropyl alcohol, dimethylsulfoxide, and acetonitrile.

The impregnated carrier material is dried and the decomposable compoundis converted to the desired active material. Usually, drying anddecomposition are separate operations, since most decomposable compoundswill be decomposed under normal drying conditions. Calcination in an airatmosphere is a preferred means of decomposing most decomposablecompounds into the desired active materials. Thus, for example, a coppersalt such as copper nitrate may be converted into copper oxide byheating the carrier particles to a temperature of about 700° to about1200° F., preferably 800° - 1000° F., in the presence of air for from 1to 6 hours, preferably about 3 hours.

The preferred copper concentration on the finished sorbent is in therange of about 2 - 10%, preferably 4 - 6% by weight.

Flue gas desulfurization sorbents comprising vanadium pentoxide onsilica can also be prepared according to this invention.

Where the desired finished product has a metal rather than a metal oxideas its active material, as, for example, platinum on alumina (which is aknown hydrogenation and hydrocracking catalyst) the metal compound(usually a metal oxide) obtained on drying and calcination is reduced tothe free metal. Suitable reducing agents are known in the art.

Catalysts and sorbents prepared as described above can be used in knowncatalytic, adsorption and cyclic chemical reaction processes. Flue gasdesulfurization, which is the preferred process of this invention, fallsinto the third category.

Removal of sulfur dioxide from a waste gas, and subsequent regenerationof the sorbent, can be carried out using a sorbent as described aboveunder known operating conditions. Thus, for example, flue gas containinga minor amount of sulfur dioxide (usually about 0.1 - 0.5% by volume ofSO₂ and typically about 0.2 - 0.3% by volume of SO₂) plus some oxygen(usually about 1-4% by volume) is passed into contact with a fixed bedof the above-described surface impregnated sorbent at a space velocityof no more than about 10,000 V/V/Hr., and usually about 1,000 to about5,000 V/V/Hr., and at a temperature which is appropriate to theparticular sorbent material used. In the case of copper oxide on aluminasorbents, the inlet temperature of flue gas as it enters the bed isgenerally about 600°-900° F., preferably about 650°-800° F. Slightlyhigher inlet temperatures, e.g., about 700°-1000° F., may be used whenthe sorbent comprises potassium oxide and vanadium pentoxide on silica,which is another known flue gas desulfurization sorbent. Thesetemperatures are typical flue gas desulfurization temperatures which areknown in the art. The active material, e.g., copper oxide, reactschemically with sulfur dioxide and oxygen. For instance, copper oxide isconverted to copper sulfate. The passage of flue gas is stopped and thesorbent is regenerated when the amount of sulfur dioxide in the effluentreaches a predetermined level. For example, if it is desired to remove90% of the amount of sulfur dioxide contained in a flue gas, thesorption or sulfation cycle is interrupted and the regeneration cycle isbegun when the total amount of SO₂ in the effluent over a whole sorptioncycle reaches 10% of the total amount of SO₂ in the entering gas.

The sorbents of this invention can be regenerated with known reducingagents and under known conditions. Suitable reducing agents includehydrogen, carbon monoxide, mixtures of these two, mixtures of eithercarbon monoxide or hydrogen (or both) with steam, and aliphatichydrocarbons such as ethane, propane, or the like, either undiluted ormixed with steam. Methane is less desirable than its higher homologuesbecause it is less reactive.

It is desirable to use regeneration temperatures which are approximatelythe same as the desulfurization temperatures, e.g., inlet temperatures,or about 600°-900° F. when a copper oxide sorbent is used. Since bothdesulfurization and regeneration are exothermic, sorbent bedtemperatures are somewhat higher than gas inlet temperatures.

Sorbents prepared according to the present invention can withstandnumerous sorption-regeneration cycles before they must be replaced.

This invention will now be described further by way of the followingexamples, which examples are included for purposes of illustrationrather than limitation.

CONTROL A

Alumina saddles (surface area 221 square meters per gram; pore volume,0.53 cc. per gram) were allowed to air hydrate overnight. (Weight drybasis 287.63 gm., weight wet basis 309.28 gm., ca. 7.0 weight percentwater pick-up.) The saddles were then immersed in 161.8 cc. of a coppernitrate solution (0.3268 gm. of CuNO₃.3H₂ O per cc. of solution),allowed to air dry overnight and then calcined for 3 hours at 800° F.The percent copper was determined to be 4.2%. A portion of the abovesorbent was tested for flue gas desulfurization (FGDS) activity in a oneinch glass unit and showed a 4.1% copper utilization at the 90% SO₂removal level.

EXAMPLE 1

Alumina saddles, which were the same as in the Control A, were soaked ina n-decyl alcohol solution, removed from the alcohol solution and dippedin a 10% HCl aqueous solution for 45 minutes. The acid dipped saddleswere then washed several times with deionized water, air dried overnightand then calcined for 3 hours at 1400° F. The saddles were allowed topick up moisture overnight and a 5.8% moisture pick-up was noted.Twenty-five of the thus processed saddles were dried for 3 hours at 650°F. and tested for pill strength (PLST). The average pill strength wasdetermined to be 10.7 lbs.

Another portion (27.05 gm. Al₂ O₃ on a dry basis) was copper impregnatedas in the Control A to give 4.6 weight percent copper. The resultantsorbent was tested in a 1 inch glass under conditions essentially as inthe Control A and showed a 7.9% copper utilization at the 90% SO₂removal level. The test conditions were as follows:

60 cc. sorbent charge

3000 V/Hr./V

2700 ppm of SO₂

650° f. temperature

EXAMPLES 2-4

Alumina saddles, as in Example 1, were similarly presoaked in decylalcohol and dipped in 10% HCl. After dipping the saddles were washedwith deionized water until the washings gave only a slight chlorinetest. The washed saddles were oven dried overnight at 230° F. andcalcined for 3 hours at 1400° F. Pill strengths for varying dip time andcompared with a control are shown in Table I.

                  TABLE I                                                         ______________________________________                                                                  Dip time      Change                                Designa-                                                                              Sorbent  Presoak  in 10% PLST   in                                    tion    type     Alcohol  HCl    (AV) lbs.                                                                            Strength                              ______________________________________                                        Control B                                                                             Alumina  None     None   13.2   --                                            Saddle                                                                Control C                                                                             Alumina  None     45 mins.                                                                              9.4   -29%                                          Saddle                                                                Example 1                                                                             Alumina  1-decan- 45 mins.                                                                             10.7   -19%                                          Saddle   ol                                                           Example 2                                                                             Alumina  1-decan- 30 mins.                                                                             13.0   -2%                                           Saddle   ol                                                           Example 3                                                                             Alumina  1-decan- 20 mins.                                                                             14.3   +8%                                           Saddle   ol                                                           Example 4                                                                             Alumina  1-decan- 10 mins.                                                                             12.2   -8%                                           Saddle   ol                                                           ______________________________________                                    

The activity gain achieved in accordance with the instant invention isshown in Table II.

                  TABLE II                                                        ______________________________________                                                 Dip Time             % Cu Utilization at                             Sorbent  in 10% HCl  % Cu     90% SO.sub.2 Removal                            ______________________________________                                        Control A                                                                              None        4.2%     4.1%                                            Example 1                                                                              45 mins.    4.6%     7.9%                                            ______________________________________                                    

CONTROL D

Alumina rings (surface area, 174 square meters per gm.; pore volume, 55cc. per gm.) were allowed to hydrate in the air overnight after a priorcalcination for 3 hours at 1400° F., resulting in a water pick-up of6.6%. The hydrated rings (339 grams) were impregnated with a coppernitrate solution (0.327 gm. Cu(NO₃)₂.3H₂ O per cc. solution), air driedovernight and then calcined for 3 hours at 800° F. The percent copper onthe alumina was 4.3%. A portion of this sorbent was tested for FGDSactivity in the 1 inch glass unit.

EXAMPLE 7

Alumina rings (as in control D) were soaked in decyl alcohol, drainedand immersed in a 10% aqueous HCl solution for 45 minutes. After washingthoroughly with water and drying overnight, rings were calcined for 3hours at 1400° F. The rings were impregnated with a copper nitratesolution, as in CONTROL D. The percent copper on the alumina wasdetermined to be 4.8%. The "acid etched" sorbent was then tested forFGDS activity and the results are shown in Table III.

                                      TABLE III                                   __________________________________________________________________________                             90% SO.sub.2 Removal                                        Presoak in  Dip time    Cu-Util-                                       Sorbent                                                                              Alcohol                                                                             Wt. % Cu                                                                            10% HCl                                                                             B.T. Min.                                                                           ization                                        __________________________________________________________________________    Control D                                                                            None  4.3   None  5.7    9.1%                                          Example 7                                                                            Decyl Alco-                                                                         4.8   45 mins.                                                                            7.5   11.4%                                                 hol                                                                    __________________________________________________________________________

What is claimed is:
 1. A method of preparing a porous solid contactmaterial which comprises the steps of:(a) immersing particles of aporous solid inorganic refractory carrier material in a polar organicpresoak liquid so as to substantially completely fill the pores of thecarrier, said presoak liquid being capable of wetting the carriermaterial and capable of displacement by the acid etching solution usedin step (c) at a rate slow enough to permit control of the extent ofacid attack; (b) separating said carrier material from said presoakliquid; (c) immersing said carrier material in an acid solution, saidacid solution being substantially immiscible with said presoak liquid;(d) removing said acid solution from said carrier material; (e)impregnating the acid solution treated carrier material with animpregnating solution containing a metal compound which is decomposableinto a desired catalyst or sorbent; (f) drying said carrier material andconverting said decomposable metal compound to said desired catalytic orsorbing metal or metal oxide or a mixture of metals or metal oxides. 2.The method of claim 1, in which the carrier material is alumina.
 3. Themethod of claim 1, in which the carrier material is hydrophilic.
 4. Themethod of claim 1, in which in step (d) said acid solution is removed bywashing said carrier material with water.
 5. The method of claim 1, inwhich the active material is copper oxide.
 6. The method of claim 1,wherein said presoak liquid comprises one or more aliphatic monohydricalcohols containing 4 to 12 carbon atoms.
 7. The method of claim 1,wherein said presoak liquid is 1-pentanol.
 8. The method of claim 1,wherein said presoak liquid is 1-decanol.
 9. The method of claim 1,wherein said impregnating solution is an aqueous solution.
 10. Themethod of claim 1, wherein said acid is water soluble.
 11. The method ofclaim 1 wherein said acid has an ionization constant of at least about1.0 × 10⁻³.
 12. The method of claim 1 wherein said acid is hydrochloricacid.